The hydrodynamic rebalancing laser (HRL) procedure is an ophthalmic therapy based on the administration of subthreshold infrared (810 nm) laser light to selected areas on the retina to treat various retina diseases. Heterogeneities of tissue response are observed, including undesired retinal damages. Variations of tissue absorbance were hypothesized to cause this uneven response. Irradiation parameters (diameter=100 μm; power=1 W; irradiation time: 50 to 200 ms), location and tissue response were studied in 16 patients (20 eyes, 2535 laser spots) to discover any correlation between tissue response and normalized fundus reflectance at 810 nm. The results demonstrate a complex relationship between some pathologies and occurrences of retinal damage, but no clear correlation. One possible reason is that the resolution of reflectance images is insufficient to see "small" (40 μm or less) absorption centers, particularly deep-seated ones. Additionally, tissue parameters other than variations of the fundus optical absorption influence heat diffusion and temperature increases. Monitoring or individualizing the light dose in HRL therapy, or any similar infrared diode laser-based therapy will require more sophisticated technologies, including imaging the retina's reflectance with an improved resolution, as well as refined methods to detect complex correlations between retinal damage and specific pathologies.

The chicken embryo's chorioallantoic membrane (CAM) is widely used as an in vivo model to study the vascular effects
induced by agents administrated topically or intravenously. Hence, in the vascular plexus of this respiratory membrane,
angiogenic and anti-angiogenic agents, as well as phototoxic effects have been studied.
The main goal of this study was to characterize the capillary network of the CAM after topical administration of
dimethyl sulfoxid (DMSO), a frequently used solvent of lipophylic drugs, including potent anti-VEGF agents. The CAM
capillaries were observed between days 8 and 9 of the embryo development, with an epi-fluorescence microscope
equipped with a sensitive camera by intravenous injection of a fluorescent agent and a non-fluorescing absorber (in the
extra-embryonic cavity) to screen the tissue background fluorescence. The fluorescence images of the CAM vasculature
were then processed in order to obtain a skeleton of the vessels and capillaries. This was done to quantify descriptors
such as the number of branching points/mm2, the mean area value of the vessels network meshes, and the mean of the 3rd
quartile of the histogram of these meshes, were then extracted.
Our results demonstrate that the topical administration of an aqueous solution of 20 μl of DMSO at concentrations equal
or larger than 0.1% turned out to modify the capillary network morphology in a dose-dependent manner as compared to
the control (20 μl of 0.9% NaCl).

Time-resolved measurements of tissue autofluorescence (AF) excited at 405 nm were carried out with an optical-fiber-based spectrometer in the bronchi of 11 patients. The objectives consisted of assessing the lifetime as a new tumor/normal (T/N) tissue contrast parameter and trying to explain the origin of the contrasts observed when using AF-based cancer detection imaging systems. No significant change in the AF lifetimes was found. AF bronchoscopy performed in parallel with an imaging device revealed both intensity and spectral contrasts. Our results suggest that the spectral contrast might be due to an enhanced blood concentration just below the epithelial layers of the lesion. The intensity contrast probably results from the thickening of the epithelium in the lesions. The absence of T/N lifetime contrast indicates that the quenching is not at the origin of the fluorescence intensity and spectral contrasts. These lifetimes (6.9 ns, 2.0 ns, and 0.2 ns) were consistent for all the examined sites. The fact that these lifetimes are the same for different emission domains ranging between 430 and 680 nm indicates that there is probably only one dominant fluorophore involved. The measured lifetimes suggest that this fluorophore is elastin.

Time-resolved measurements of endogenous tissue autofluorescence were carried out on the bronchial mucosa of 18 patients during endoscopy by the means of a optical fibre-based spectrometer. The objective was to assess the fluorescence lifetime as a new contrast parameter between normal and malignant tissue and to explain the origin of a previously observed contrast in fluorescence intensity. The intra- and interpatient variation of tissue autofluorescence intensity and decay on normal tissue was determined with the outcome that a strong fluctuation in autofluorescence intensity but not in lifetime was observed on the normal tissue. Preliminary results were obtained by comparing fluorescence decays on normal mucosa and dysplasia/carcinoma in situ. No significant change in fluorescence decay nor in spectrum between 510 and 650 nm was found. Measurements in parallel with an endoscopic autofluorescence imaging device, on the other hand, indicated a contrast in intensity and spectrum on the same lesions. This suggests that the spectral contrast might be due to an enhanced blood concentration in deeper lying layers of the lesion the optical fibre-based contact measurements are less sensitive to. The difference in intensity might be due to a lower concentration in fluorophores or to the thickening of the epithelium in the neoplastic mucous membrane. However, no indication for fluorescence quenching in the upper layers of the mucous membrane as the reason for the reduced fluorescence intensity was found. The fluorescence decays showed a quite stable behaviour with three decay times of 6.9 ns, 2.0 ns and 0.2 ns in the spectral range between 430 and 680 nm. This can be an indication that there is one dominant fluorophore involved, the calculated decay times suggest that it might be elastin. However, a slight spectral dependence of the fluorescence decays let presume that there is a contribution from other fluorophores, probably flavins and NADH.

The biomedical use of an optical fiber-based spectro- temporal fluorometer that can endoscopically record the fluorescence decay of an entire spectrum without scanning is presented. The detector consists of a streak camera coupled to a spectrograph. A mode-locked argon ion pumped dye laser or a nitrogen laser-pumped dye laser are used as pulsed excitation light sources. We measured the fluorescence decays of endogenous fluorophores and of ALA-induced- protoporphyrin IX(PPIX) in an excised human bladder with a carcinoma in situ (CIS). Each autofluorescence decay can be decomposed in at least three exponential components for all tissue samples investigated if the excitation is at 425 nm. The decays of the autofluorescence of all normal sites of the human bladder are similar and they differ significantly from the decays measured on the CIS and the necrotic tissue. The fluorescence of the ALA-induced PPIX in the bladder is monoexponential with a lifetime of 15 (plus or minus 1) ns and this fluorescence lifetime does not change significantly between the normal urothelium and the CIS. A photoproduct of ALA-PPIX with a fluorescence maximum at 670 nm and a lifetime of 8 (plus or minus 1) ns was observed. The measurement of the decay of the autofluorescence allowed to correctly identify a normal tissue site that was classified as abnormal by the measurement of the ALA-PPIX fluorescence intensity.

The design and characterization of optical phantoms which have the same absorption and scattering characteristics as biological tissues in a broad spectral window (between 400 and 650 nm) are presented. These low cost phantoms use agarose dissolved in water as the transparent matrix. The latter is loaded with various amounts of silicon dioxide, intralipid, ink, bovine serum, blood, azide, penicillin and fluorochromes. The silicon dioxide and intralipid particles are responsible for the light scattering whereas the ink and blood are the absorbers. The penicillin and the azide are used to insure the conservation of such phantoms when stored at 4 degrees Celsius. The serum and fluorochromes, such as Coumarin 30, produce an autofluorescence similar to human tissues. Various fluorochromes or photosensitizers can be added to these phantoms to simulate a photodetection procedure. The absorption and fluorescence spectroscopy of the dyes tested was not different in these phantoms than in live tissues. The mechanical properties of these gelatinous phantoms are also of interest as they can easily be molded and reshaped with a conventional cutter, so that for instance layered structures, with different optical properties in each layer, can be designed. The optical properties of these phantoms were determined between 400 and 650 nm by measuring their effective attenuation coefficient ((mu) eff) and total reflectance (Rd). The microscopic absorption and reduced scattering coefficients ((mu) a, (mu) s') were deduced from (mu) eff and Rd using a Monte-Carlo simulation.

Fluorescence and Raman spectroscopic analysis has been developed at the subcellular level, using laser excitation under the microscope. This approach has been successfully used on single living cells to monitor different biological molecular processes. The experimental applications which are presented here give an illustration of the performance of the method to obtain kinetic, topographic (spectral imaging), or quantitative data.

Biophotonic excitation of purine and pyrimidine nucleobases becomes of increasingly importance as the laster intensity increases. Under these conditions the overall energy absorbed is much higher than the threshold energy required to generate pyrimidine and purine cathion radicals estimated to lies iin the 5-5.5 eV range (1). It is now communly accepted that the cathion radical is the primary damaging species generated upon two-quantum laser photolysis of nucleic acids derivatives. The chemistry of pyrimidine and purine cathion radicals in aqueous solutions has not been well udnerstood until recently. Two major exception delt with the initial chemical reaction of photo and ratioation - induced radical cation in low temperature thymine and thymidine - 5 - phosphate (2, 3) and at room temperature where the pyrimidine radical cathions were generated through an electron transfer reaction to photoexcited mendione in a triplet state.

Polarization and lifetime studies have shown that the fluorescence from nucleic acid species is complex, both at the individual chromophore level and because of the effect of stacking interactions on the electronic states. Recent work aimed at elucidating some aspects of this behavior by decay analysis and time-resolved spectroscopy is surveyed. Experimental work has been carried out using the ACO synchrotron at LURE (France) with time-correlated single photon counting, or a frequency-doubled N2-pumped dye laser, pulse width 700 ps, with fast-gated (100 ps width) analog detection and signal averaging. Decay curves are treated by global analysis using the Marquardt non-linear least-squares algorithm (synchrotron data) or the SPLMOD program (EMBO), which carries out a non-linear leastsquares minimization using cubic splines, for the laser data. Resolution of the decay data gives a model-based estimate of the number of components and their lifetimes. This information is then used to deconvolute timewindowed spectra (time-delayed spectra) into the time-resolved spectra. It is a particular feature of the combination of delayed photon counting with the continuous wavelength distribution of pulsed synchrotron radiation that excitation spectra correlating with emissions of different lifetimes can be obtained by uninterrupted repetitive scanning over a wide range of exciting wavelengths, in the present work from 230 nm to 354 urn. Such time-delayed excitation spectra can also be deconvoluted into components corresponding to the various time-resolved emission spectra. Examples of these three types of information viz resolved lifetimes, time-resolved emission spectra and their excitation spectra are presented and discussed for the following systems. I. adenosine; 6N, 6N-dimethyladenosine; protonated adenosine; this work shows the role of rotamers in the excited state behavior of this chromophore and demonstrates the forbidden nature of the lowest excited state. II. d(AT); d(TA); we observe the sequence dependence of emission from the stacked state which has been observed previously in polarization studies and an unusual excitation spectrum. III. d(CG); poly d(CG), "B"-DNA structure; single crystal duplex d(CG)3, "Z"-DNA structure. Distinctive differences are observed between the stacked emissions from the "B" and "Z" structures which we attribute to different overlapping of the stacked bases.

My Library

You currently do not have any folders to save your paper to! Create a new folder below.

Keywords/Phrases

Keywords

in

Remove

in

Remove

in

Remove

+ Add another field

Search In:

Proceedings

Volume

Journals +

Volume

Issue

Page

Journal of Applied Remote SensingJournal of Astronomical Telescopes Instruments and SystemsJournal of Biomedical OpticsJournal of Electronic ImagingJournal of Medical ImagingJournal of Micro/Nanolithography, MEMS, and MOEMSJournal of NanophotonicsJournal of Photonics for EnergyNeurophotonicsOptical EngineeringSPIE Reviews